(Received 21 November 2012;accepted 13 December 2012;online 22 December 2012)

In the title mol­ecule, C36H39ClN4OS, the non-aromatic part of the cyclo­hex-1-enyl ring and the attached tert-butyl group are disordered over two conformations with occupancy ratios of 0.52 (3):0.48 (3) and 0.53 (3):0.47 (3), respectively. The polyene chain single- and double-bond dimensions contrast with a closely related compound [Bouit et al. (2007). Chem. Mater.19, 5325–5335] with an approximate 19° twist between donor and acceptor ends of the mol­ecule, related to the additional intra­molecular C—H⋯S inter­action. In the title compound, the mol­ecules pack into dimeric units about centres of symmetry utilizing weak C—H⋯N(cyano) and C—H⋯O attractive inter­actions, building both chain and ring motifs about the centres [R22(8) and R22(9)]. Adjacent dimeric sets then form a herringbone configuration.

The title compound, C36H39ClN4OS (3, Figure 1) was synthesized as part of our ongoing research involving the development of organic nonlinear optical (NLO) chromophores. As part of this we have previously reported the crystallographic parameters for chromophores containing an indoline donor coupled to a 2-(3-cyano-4,5,5-trimethyl-5H-furan-2-ylidene)-malononitrile electron acceptor group (Bhuiyan et al., 2011). Compound 3 was synthesized to check the impact of using a benzothiazole based donor as this should influence both the degree of both length alternation (viz. bond order) as well as the crystal packing. Compound 3 was conveniently prepared in good yield by the condensation of N-pentyl-2-methylbenzothiazolinium iodide 1 with precursor 2 (Figure 1). Compound 2 was prepared by the procedure previously reported in the literature (Kay et al., 2004).

Compound REFCODES are from the C.S.D. (Version 5.33, with August 2012 updates; Allen, 2002). The asymmetric unit contents of the title compound(I) are shown in Figure 1. The 5-membered ring plane of atoms O1,C4—C7 (hereafter "CDFP", [3-cyano-5,5-dimethyl-2,5-dihydrofuran-2-ylidene]propanedinitrile) can be regarded as planar with maximum out of plane deviation for C4 of 0.029 (4) Å. The dicyano group (N1,C1,C2,C3,N2,C6) is planar but twisted by 9.4 (3) ° with respect to the "CDFP" group; this is similar to the twist in related compound NOJKUT (Gainsford et al., 2008) of 5.69 (17)°, and is consistent with alleviating intramolecular contacts with the cyano group (C10–N3). The benzothiazol-2-ylidene fused ring is approximately planar with maximum out of plane distance for N4 0.026 (3) Å. This plane makes an angle of ~7° to the polyene chain atoms (C13—C16,C23,C24), which in turn is ~18° from the "CDFP" plane. These twists in the adjacent near-planar moieties contrasts with the closely related molecule HITVIQ (Bouit et al.,2007) where the benzothiazole entity is replaced by a 1-benzyl-3,3-dimethyl-1,3-dihydro-2H-indol-2-ylidene: here the CDFP and terminal donor rings make an angle of ~10°. As in HITVIQ, there are close intramolecular H···Cl interactions involving the adjacent polyene hydrogen atoms (entries 7 & 8, Table 1) but here there is an additional H···S interaction (2.68 Å, entry 9, Table 1) contributing to the twist.

The different deviation from molecular planarity is also reflected in a significant difference between the two structures in the alternation of double and single bonds beginning at the C2–C6 CDFP bond (Table 2). This alternation is described by the BLA parameter (Marder et al., 1993), reflecting the average change in bond length alternation. A related sodium salt (with the CDFP ring at both ends of the molecule EGOSOJ, Bouit et al., 2008)) appears to be have intermediate BLA values between the two.

The molecules pack into dimeric units about centres of symmetry utilizing weak C–H···Cyano(N) and C–H···O attractive interactions, building both chain and ring motifs about the centres (R22(8) & R22(9)). Table 2 summarizes those attractive interactions and key elements are shown in Figure 3. The adjacent dimeric sets then form a typical "herringbone" configuration. In contrast, the HITVIQ molecules have mainly weak, close to in-plane interactions (C–H···Cl), linked via chain motif weak C–H···N(cyano) interactions.

Nine reflections affected by the backstop and 12 others which were clearly outlier data (mostly at low angle) were omitted from the refinements (using OMIT). The methyl and other H atoms were refined with Uiso 1.5 & 1.2 times respectively that of the Ueq of their parent atom. All H atoms bound to carbon were constrained to their expected geometries (C—H 0.95, 0.98 & 0.99 Å).

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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